Control system



- 5, 1944- e. B. STARlE ETAL CONTROL SYSTEM Filed Dec. 14, 1943 ,2 ml 5:Pm we 5 a n Ptc r 2 n M n r w mi N S W PatentedDec. 5, 1,944

UNITED STATES PATENT OFFICE 2,364,fl86 CONTROL SYSTEM George B. Starie,Schenectady, and Anton W. Schmitz, Scotia, N. Y., assignors to GeneralElectric Company, a corporation of New York I Application December 14,1943, Serial No. 514,224

4 Claims.

This invention relates to control systems, more particularly tofollow-up control systems, and it has for an object the provision of asimple, reliable, and improved control system of this character.

Another object of this invention is the provision of an inexpensivefollow-up control system having a high degree of accuracy.

In carrying the invention into etiect in one form thereof, twopotentiometers are provided, of which oneis the master potentiometer andthe other is the follow-up potentiometer and is driven by an electricmotor. The direction and amount of rotation of the follow-up motor arecontrolled by a pair of electromagnetic switching devices which arecontrolled by the difierential voltage between the two potentiometers.Each of the two electromagnetic switching devices is provided with amain operating coil and with an auxiliary operating coil. In the normalor deenergized condition of the apparatus, the main operating coils ofboth potentiometers are connected in series relationship across a sourceof supply, and the auxiliary coils are connected in series relationshipbetween the voltage pickoff points of the two potentiometers so as to beresponsive to the differential voltage between these two pickofi points.The polarity of the coils of these electromagnetic switching devices issuch that for one polarity of the difierential voltage, the main andauxiliary coils of one or the switching devices are additive and thoseof the other device are subtractive or bucking. For the reverse polarityof the differential voltage, the coils of the second switching deviceare additive and those of the first switching device are subtractive.Each switching device in pickin up deenergizes its main operating coilso that the dropout can be efiected in response to the decrease of thpotentiometer differential voltage. Additionally, each electromagneticswitching device in picking up short circuits the auxiliary coil of theother switching device so that the switching device which is picked 'upcan be made to drop out at a predetermined low value of the difierentialvoltage to stop the motor with the driven potentiometer in accuratecorrespondence with the master potentiometer.

For-a better and more complete understanding of the invention, referenceshould now be had to the following specification and to the accompanyingdrawing of which the single figure is a simple, schematic diagram of anembodiment of the invention.

In illustrating the invention in one form thereof, it is shown asembodied in a control system a rapid initial rate.

for accurately presetting the operating speed of a motor on a masterpotentiometer, and maintaining the speed of the motor at a valuecorresponding to the preset value.

Referring now to the drawing, it is desired to preset the operatingspeed of a motor In while the motor is at rest or operatin at somedifierent speed, and subsequently to cause the speed of the motor tochange to the preset speed and be maintained at that speed. The speed ofthe motor is preset on a master potentiometer H which is provided with adial Ha calibrated in terms of speed.

The motor It is supplied from a suitable source, such as the adjustablevoltage generator l2, which is driven at a suitable speed, which ispreferably substantially constant, by any suitable driving means, suchas an induction motor (not.

shown). As shown, the motor is provided with a field winding llla whichis separately excited from a suitable source, such as represented by thesupply lines 13, id.

- The generator i2 is provided with a separately excited field winding32a which is excited from a cross armature flux excited, direct armatureflux compensated dynamoelectric machine 15, which is provided with amain reference control field winding i5a and a voltage control fieldwinding i511. The reference field winding ifia is excited from asuitable source of constant excitation, such as the supply lines l 3,id, and the voltage control windin ibb is excited from the voltage ofthe generator 52. The reference field winding i511. is polarized in adirection to increase the voltage of the generator 12, and the voltagecontrol field winding 151: is polarized in a direction to decrease thegenerator voltage. Thus, the voltage of the generator i dependent on thedilference of the excitation of the two field windings i5a and 55?).When the -voltage of the generator 12 i zero, the excitation of thevoltage control field winding 15b is also zero, so that the referencefield winding is unopposed and the net excitation of the dynamoelectricmachine i5 is maximum. Maximum excitation of the machine 15 causes thegenerator voltage to rise at Increasing the generator voltage increasesthe excitation of the field winding I512, so that the net excitation ofmachine 15 decreases. The voltage of the generator [2 continues toincrease but at a decreasing rate until a balanced condition isestablished such that any further decrease in the net excitation of thedynamoelectric machine 15 would result in a decrease in the voltage ofthe generator I 2.

For the purpose of adjusting the voltage of the generator l2, a rheostatH5 is included in series relationship with the voltage control fieldwinding l5b. The greater the amount of resistance that is included inthe circuit with the voltage control field winding l5b, the higher mustthe voltage of the generator l2 rise in order to bring about thebalanced condition just described. Thus, by adjusting the rheostat Hi,the voltage of the generator l2 and the speed of the motor l0 can becorrespondingly adjusted,

In order to control the rate at which the speed of the motor, I0 ischanged from zero to a preset value, or from one preset value toanother, the slider lfia of rheostat I6 is preferabl driven at asubstantially constant speed by an electric motor l! which is suppliedfrom a suitable source, such as the source l3, l4. The rheostat l6 mayhave as many as 100 buttons to provide 100 different speed settings ofthe motor l0, although a smaller number is shown in the drawing.

The motor I! is utilized as the driving means of a follow-up controlsystem to move the slider lBa to a position on the resistor Is at whichthe speed of the motor l0 will correspond to the speed preset upon themaster potentiometer ll. As shown, the master potentiometer ll isconnected across the supply source l3, l4.

Also included in this follow-up system is a potentiometer l8 which isconnected across the source l3, l4 and is provided with a slider l8awhich is driven by the motor H.

.The rotation of the motor I! is controlled by suitable electromagneticcontactors l9 and which, in turn, are controlled by the electromagneticswitching devices 2l and 22, respectively.

ity of the difierential voltage between the slider 'l lb of the masterpotentiometer I I and the slider l8a of the following potentiometer IS.

The switching devices 2| and 22 are provided with main operating coils2la and 22a, respectively, connected in series relationship across thesource l3, l4 and with auxiliary coils 2lb and 22b, respectively,connected in series relationship between the slider llb of the masterpotentiometer l l and the slider l8a of the follow-up potentiometer l8.Capacitors 2lf and 221 in parallel with main operating coils Zla and 22arespectively maintain the energizations of these coils immediatelyfollowing the opening of contacts 2lc and 220, thereby to insure closureof these contactors. The polarity of the coils on these two switchingdevices is such that when the voltage of the slider llb is negative withrespect to the voltage of the slider l8a, the coils 21a and 2lb areadditive, and the coils 22a and 22b of the switching device 22 aresubtractive or bucking.

For the purposes of illustration it may be assumed that the switchingdevices 2| and 22 pick up their armatures in response to an excitationof 360 ampere turns and drop out their armatures at an energization of36 ampere turns. It may also be assumed that the main coils 2 la. and22a each produce 270 ampere turns of the 360 ampere turns required forpickup, and that the coils Zlb and 22b each produce the remaining 90ampere turns of the 360 required for pickup. It may further be assumedthat each of the coils Zlb and 22b has 1280 turns and nine ohmsresistance. Since each of the coils 2 lb and 22b has 1280 turns and eachmust produce ampere turns for pickup, the current which must flow inthese coils to produce 90 ampere turns is 0.07 ampere. Further, sinceboth coils 2 lb and 22b are connected in series relationship between thesliders l lb and l8a, and since the total resistance of both coils inseries is 18 ohms, the differential voltage between the sliders llb andl8a required to cause 0.07 ampere to flow through the coils is 1.26volts.

An additional potentiometer 23 is provided for presetting a lowthreading speed for the motor l0. For the purpose of selectivelypreparing a circuit between the slider llb or slider 23a and slider lllato initiate the operation, an electromagnetic contactor 25 and asuitable switching device illustrated as a manually operated momentarycontact type push-button switch 26 for controlling the contactor 25 areprovided. To complete the connection between the slider 23a or theslider l lb and the slider l8a of the followup potentiometer, acontactor 2'! under the control of a push-button type switch 28 isprovided.

The acceleration of the motor Ill from zero to a preset speed, or fromone preset speed to another, may be interrupted after initiated by meansof a switching device 29, and an electromagnetic contactor 30 controlledthereby for interrupting the connection between either the masterpotentiometer l l or the threading potentiometer 23 and the follow-uppotentiometer l8.

With the foregoing understanding of the elements and their organization,the operation of the system itself will readily be understood from thefollowing detailed description. The switches 3i and 32 are closed tocomplete the connections of the supply lines l3, M to a suitable sourceof D. C. voltage. The field winding lfla of the motor l0 and the fieldwinding l'la of the motor I], which are connected across the supplylines l3, l4, are thus energized. The circuit of the reference fieldwinding l5a of the dynamoelectric machine I5 is interrupted at thenormally open contacts 270 of contactor 27. Consequently, the machine l5generates zero voltage, and likewise. the voltage of the generator l2,which is excited from the machine I5, is zero. The driving motor H] istherefore at rest.

In the deenergized condition of the apparatus the slider l8a is in itsextreme left-hand position in which it moves the movable contact member33a of the limit switch 33 into engagement with the stationary contact331), thereby to complete an energizing circuit for the operating coilof the stop contactor 34. This energizing circuit ex-- tends from thesupply line [3 through the normally closed contacts of the stoppush-button switch 35, contacts 33a and 33b of the limit switch,operating coil of contactor 34 to the side It o1- the source. Inresponse to energization, contactor 34 closes its main contacts 34a andalso closes its lower interlock contacts 341) to complete a sealing-incircuit which is independent of the contacts of the limit switch.

The speed at which it is desired tooperate the motor I!) is preset uponthe master potentiometer ll by moving the slider llb to a point on thepotentiometer corresponding to the desired speed as indicated upon thecalibrated dial I la. Thereafter, the run push-button switch 26 ismomentarily depressed to complete an energizing circuit for theoperating coil of the contactor 25. This circuit extends from the sidel3 of the source through the contacts ing device 2| is in 34a of thestop contactor 34 (in the closed position thereof), through the uppernormally closed contacts of the thread push-button switch 28, contacts281; of the pushbutton switch 26,'operating coil 25a of contactor 25 tothe opposite side ll of the supply source. Contactor 25 responds andcloses its contacts 25b to complete a sealing-in circuit for its coilindependent of the contacts of the push button switch 26 which may nowbe released. Simultaneously, contactor 25 closes its normally opencontacts 250 and 25d and opens its normally closed contacts 256.

The closing of contacts 250 completes an energizing circuit for theoperating coil 21a of the start contactor 21 which picks up in responseto energization and seal itself in through contacts 21b. In picking up,contactor 21 also closes its normally open contacts 21c, 21d, 212 andopens its normally closed contacts 21f.

The closing of contacts 25d and 27d completes the connections from theslider l lb of the potentiometer ll through the auxiliary coils 2| b and22b of switching devices 2| and 22, respectively, to the slider Hill ofthe follow-up potentiometer I 8. If. the slider I lb has been moved to aposition on the potentiometer ll such that the differential voltagebetween the slider llb and the slider l8a is at least 1.26 volts, theampere turns of the auxiliary coil 2lb added to the ampere turns of themain operatin coil Zla of switching device 2| will be sufiicient to pickup the switching device 2|. In the position in which the slider llb isillustrated in the drawing, the differential voltage between the sliderllb and the slider |8a may be assumed to be greatly in excess of 1.26volts-and therefore the switching device 2| picks up to open itsnormally closed contacts 2lc and close its normally open contacts 2|dand Zle. Since the ampere turns of the operating coil 22b aresubtractive with respect to the ampere turns of the main operating coil22a, the switching device 22 is not picked up.

Contacts 2Ie in opening interrupt the energizing circuit for the mainoperating coil 2 la. However, since the ampere turns produced by theauxiliary coil2 lb required to pick up the switchexcess of the dropoutampere turns, the switching device 2| remains picked up. The closing ofthe contacts Zld short circuits the auxiliary coil 22b of switchingdevice 22, and consequently, the ampere turns of the auxiliary coil 2lbare doubled.-

Contacts 2|e in closing complete an energizing circuit for the operatingcoil of the directional contactor 9 which is readily traced from theside l3 of the supply source through the normally closed contacts 30a ofcontactor 30, contacts 27c of start contactor 21, contacts 2|e ofswitching device 2|, normally closed contacts of limit switch 35,contactor l9 to the side It of the source. Responsively to energization,contactor l9 picks up and opens its normally closed closes its normallyopen contacts |9b to connect the armature of the motor l to the sourcel3, l4 for rotation in a direction to move the sliders Ilia and |8a tothe right.

As the slider lBa moves to the right, the differential voltage betweenthe slider Ill) and the slider |8a is decreased, and the'ampere turns ofthe auxiliary Winding 2lb of switching device 2l are correspondinglydecreased. Since the dropout value of the relay 2| is 36 ampere turns,and since the auxiliary coil 2lb has 1280 turns, the switchand operatingcoil of right directional contacts |9a and I I ture of the motor ll.

slider lb 2| will drop out when the slider |8a reaches a position on thepotentiometer l8 which differs from a position of exact correspondencewith the position of the slider llb on the master potentiometer H by anamount which corresponds to approximately one-fourth of a volt on thefollowup potentiometer H3.

The dropping out of the switching device 2| interrupts the energizingcircuit for the operating coil l9a of the contactor l9. Responsively todeenergization, contactor l9 drops out to disconnect the motor II fromthe source l3, l4, and also closes its normally closed contacts 48a tocomplete a dynamic braking circuit for the arma- As a result, the motorll is brought to rest with the slider |8a in a position which difiersfrom a position of correspondence with respect to the position of theslider llb by an amount which is equal to or less than an amountcorresponding to one-fourth of a volt on the potentiometer l8.

The movement of the slider l8a to this new position corresponding to thepreset position of the slider llb also moves the slider lfia to acorresponding position on the rheostat l6, which corresponding positionmay be assumed to be represented by the button Kid.

The closing of contacts 270 in response to the closing of the startcontactor 27 completes the connections of the reference field winding l5of dynamoelectric machine l5 to the supply source l3, l4. As a result ofthe excitation of the reference field winding l5a, and the movement ofthe slider |6a to the button |6d on the rheostat l6, the voltage of thegenerator l2 is increased to a value corresponding to the position ofthe of master potentiometer ll, and the motor H] is accelerated to acorresponding speed.

If the auxiliary coil 22b had not been short circuited by the contacts2| (1 when switching de vice 2| picked up, the current in the coil 2lbwould have decreased to the dropout value when the differential voltagebetween the sliders decreased to 0.504 volt. Consequently, the motor l1would have stopped with the slider |8a in a position which differs froma position of exact correspondence with respect to the position ofslider llb by an amount corresponding to approximately one-half volt Onthe potentiometer |8.' In other words, if the auxiliary coil 22b had notbeen short circuited, the error in the stopping position of the sliderl8a would have been twice as great. In practice, the distance betweenthe'buttons on the rheostat I6 is less than the length of a portion ofthe potentiometer i8 which corresponds to a voltage of one-quarter volt.Thus, it will be seen that the follow-up system results in stopping theslider lBa on that button contact of the potentiometer l6 whichcorresponds most exactly to the position of the slider l lb on themaster potentiometer.

If it is desired to decrease the speed from the preset value to a lowervalue, the slider lb may be moved in a counterclockwise direction to aposition corresponding to the desired low speed, such for example asrepresented by the position of the dotted line i la. As a result, thecurrent flow through the auxiliary coils 2lb and 2222 will tactor(closed in the left limiting position),

be in the reverse direction as compared with the direction of currentflow when the slider I lb was moved in the clockwise direction. Thus,the ampere turns of the auxiliary coil 22b will be additive with respectto the ampere turns of the main operating coil 22a and, consequently,the switching device 22 will pick up to open its normally closedcontacts 220 and close its normally open contacts 22d and 22e. ContactsHe in opening interrupt the energizing circuit of the main operatingcoil 22a, and contacts 22d in closing short circuit the auxiliaryoperating coil 2!!) of switching device 2|. The closing of contacts 22ccompletes an energizing circuit for the left directional contactor 20which, responsively to energization, picks up and closes its normallyopen contacts to connect the armature of the motor II to the source I3,II, for rotation in a direction to move the sliders 16a and Illa to theleft. When the slider i8a reaches a position of correspondence withrespect to the position of the slider lib, the motor 11 is stopped andthe slider l6a comes to rest on a button corresponding to the positionof the slider I lb. Consequently, the voltage of the generator 12 isdecreased to a corresponding value' and the speed of the motor I isdecelerated to a corresponding value.

To stop the motor [0, the stop push button 35 is depressed to interruptthe energizing circuit for the operating coil of the stop contactor 34.In response to deenergization, the stop contactor 34 opens its contacts34a to interrupt the energizing circuit for the operating coils of therun contactor 25 and the start contactor 21, and these contactors inresponse to deenergization drop out to the positions in which they areillustrated in the drawing. In the dropped out position of the contactor21, an energizing circuit for the operating coil of the left directionalcontactor 20 is completed which extends from the side l3 of the supplysource through normally closed contacts 21] of contactor 21, contacts330 of limit switch 33 (bridged by the movable contact member 33a whenthe slider |8a was moved to the right), operating coil of contactor 20to the side M of the source. Responsively to'energization, contactor 20picks up and closes its normally open 'contacts to connect the motor I!to the supply source l3, l4 for rotation in a direction to move thesliders Na and l8a toward the left. At the extreme left limit of travelof the sliders Mia and l8a, the movable contacts 33a of the limit switch33 are moved out of engagement with the stationary contacts 330, therebyto interrupt the energizing circuit for the operating coil of contactor20. In response to deenergization, contactor 20 disconnects the motor I!from the supplysource and the normally closed contacts of contactor 20complete a dynamic braking circuit for the armature of the motor H. Thesystem is now in a reset condition.

If in starting up from rest, it is desired to operate the motor IO at alow threading speed, this may be accomplished by moving the slider 23aof the threading potentiometer to a position corresponding to thedesired low threading speed. The thread push-button switch 28 is thenmomentarily depressed to bridge the normally open contacts 220. tocomplete an energizing circuit for the operating coil of the startcontactor 21, which circuit is traced from the side l3 source throughthe contacts 34a of the stop conwhen the sliders lBa and Mia arecontacts 23a of push button switch 28, operating coil 21a to the side ofthe supply v H of the source. In response to energization, the startcontactor 21 picks up and closes its normally open contacts 21b, 21c,21d, and 21c and opens its normally closed contacts 21 The run contactor25 is not picked up and consequently its normally closed contacts 25cremain closed. Thus, a connection is completed between the slider 23a ofthe threading potentiometer 23 and the slider I8a of the follow-uppotentiometer I8 through the contacts 256, contacts 21d of startcontactor 21, normally closed contacts 30d of close contactor 30,auxiliary coils 2lb and 22b to the slider l8a. As a result, the motor [Iwill be started and the sliders I81: and 16a moved to positionscorresponding to the position of the slider 23a of the threadpotentiometer in a manner similar to the operation described in theforegoing, and the motor ID will be accelerated to a correspondingspeed.

Although in accordance with the provisions of the patent statutes thisinvention is described as embodied in concrete form and the principlethereof has been explained, together with the best mode in which it isnow contemplated applymg that principle, it will be understood thatmodifications and alterations will readily occur to persons skilled inthe art without departing from the spirit of this invention or from thescope of the annexed claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A follow-up control system comprising in combination, a masterpotentiometer, a driven potentiometer, a motor for driving said drivenpotentiometer, means responsive to a differential voltage between saidpotentiometers for controlling said motor to drive said drivenpotentiometer toward a position of zero differential voltage withrespect to said master potentiometer comprising a pair of switchingdevices each provided with a main coil and an auxiliary coil,connections for connecting said main coils in series to a source,connection for connecting said auxiliary coils in series relationshipbetween said p otentiometers, the coils of one of said switching devicesbeing connected for an additive relationship, and the coils of the otherof said switching devices being connected for a differentialrelationship in response to a differential voltage of one polaritybetween said potentiometers thereby to provide for selective operationof said switching devices to effect rotation of said motor in adirection corresponding to the polarity of said differential voltage,and means responsive'to operation of each of said switching devices fordeenergizing the main coil thereof.

2. A follow-up control system comprising in combination, the masterpotentiometer, a. driven potentiometer, a motor for driving said drivenpotentiometer, means responsive to a differential voltage between saidpotentiometers for controlling said motor to drive said drivenpotentiometer toward a position of zero differential voltage withrespect to said master potentiometer vided with a main coil and anauxiliary coil, connections for connecting said main coils in series toa source, connections for connecting said auxiliary coils in seriesrelationship between said potentiometers, said connections providing anadditive relationship of the coils of one of said switching devices anda differential relationship of the coils of said other switching devicein response to a differential voltage of one polarity between saidpotentiometers thereby to provide for selective operation or saidswitching devices to eiIect a rotation of said motor in a directioncorresponding to the polarity of said diil'erential voltage, and meansresponsive to operation of each of said switching devices fordeenergizing the'aux iliary coil of the other of said switching devices.

3. A follow-up control system comprising in combination, a masterpotentiometer, a driven potentiometer, a motor for driving said drivenpotentiometer, means responsive to a difierential voltage between saidpotentiometers for controlling said motor to drive said drivenpotentiometer toward a position of zero diil'erential voltage withrespect to said master potentiometer comprising a pair of switchingdevices each provided with a main coil and'an auxiliary coil,connections for connecting said main coils in series to a source,connections for connecting said auxiliary coils in series relationshipbetween said potentiometers, the coils of one of said switching devicesbeing connected for an additive relationship and the coils of the otherof said switching devices being connected for a diiferentialrelationship 'inresponse to a diflerential voltage of one polaritybetween said potentiometers thereby to provide for selective operationof said switching devices to eirect rotationof said motor in a directioncorresponding to the polarity of said din'erential voltage, and meansresponsive to operation of each oi said switching devices fordeenergizing the main coil thereof and the auxiliary coil'oi' the otherof said switching devices thereby to stop said motor in response to apredetermined low value 01' said diil'erential voltage.

aseecsc 4. .A follow-up control system comprising in combination, amaster potentiometer provided with a slider, a driven potentiometerprovided with a slider, an electric motor for driving the slider. ofsaid driven potentiometer, means responsive to a diflerential voltagebetween said sliders for energizing said motor to drive said drivenslider toward a position of zero differential voltage with respect tothe slider of said master potentiometer comprising a pair of switchingdevices each provided with a main coil and an auxiliary coil,connections for connecting said main coils in series to a source,connections for connecting said auxiliary coils in series relationshipbetween said sliders, said connections providing for an additiverelationship of the coils of one of said switching devices and a.differential relationship of the coils of the other of said switchingdevices in response to a voltage of one polarity between said slidersthereby to provide for selective operation of said switching devices toeffect rotation of said motor in a direction corresponding to thepolarity of said differential voltage, and means responsive to operationof each of said switching devices for deenergizing the main coil thereofand the auxiliary coil of the other of said devices to stop said drivenslider at a point of substantially zero potential diflerence withrespect to the slider of said master potentiometer.

GEORGE E; STARIE. ANTON W. SCHMI'I'L.

